serial section, although a single cell rarely occurred in more than one 

 section. This concentration varied little over the length of a given 

 filament. Individual mucus cells appeared to be less than 6 micrometers 

 in diameter. 



Many mucus goblet cells appeared on the gills of white perch exposed 

 to fuller's earth concentrations (Fig. 3). In some cases mucus cells were 

 the only visible cellular component of the tissue at the anterior margin 

 of the filaments. The mucus cells were confined to the margins of the 

 filaments, particularly to the anterior margin which is the first to come 

 in contact with the water. Little, if any, increase in mucus cell con- 

 centration was observed elsewhere in the gill. Examination of serial 

 sections revealed no increase in the size of individual mucus cells. High 

 mucus cell concentrations made identification of individual cells difficult. 



The secondary lamellae on the gill sections of white perch consisted 

 of a supportive tube of pilar cells with red blood cells present inside 

 the tube. A single, thin layer of epithelium covered the lamellae (Fig. 4). 

 The integrated structure of the secondary lamellae provides for maximum 

 respiratory gas exchange efficiency by maintaining a minimum distance 

 between the hemoglobin-rich red cells and the oxygen-rich water. 



The secondary lamellae of white perch exposed to 0.65 g 1"-^ fuller's 

 earth were swollen. The epithelium was separated from the pilar cell tube 

 and the epithelial cells were enlarged, forming a thick covering (compare 

 Figs. 4 and 6). Pilar cell structure usually remained intact (Fig. 5), 

 although it was occasionally disrupted (Fig. 6). 



The effects of fuller's earth suspensions on gill tissues of white 

 perch were similar to the effects of diatomaceous earth on rainbow trout 

 gills (Southgate, 1962) and the effects of china-clay mining waste on 

 brown trout gills at high concentrations (Slanina, 1964) and low concen- 

 trations (Herbert, et al . , 1961; Herbert and Merkens, 1961). 



The gills of fish exposed to suspended solids showed separation of the 

 epithelium from the lamellar structure, thickening of the epithelium, and 

 occasional disruption of the pilar cell structure of the lamellae (Herbert 

 and Merkens, 1961; Herbert, et al., 1961; Southgate, 1962; Slanina, 1964). 

 These effects were induced using concentrations of suspended solids between 

 0.40 and 0.81 g 1"-^, with a high percentage of particles in the silt-clay 

 range. The effect of particle size on gill tissue has not been fully 

 evaluated. However, based on available data, a definite concentration 

 effect is associated with silt-clay-sized particles. Concentrations of 

 fuller's earth below the 24-hour LC^o value may adversely affect the gill 

 tissue structure of the white perch in a 5-day period. 



Gill damage caused by suspended solids has not been positively iden- 

 tified as harmful to fish in terms of overall survival. Ritchie (1970) 

 pointed out that the type of gill damage caused by particles in suspension 

 effectively reduces the respiratory surface area. He stated that a reduced 



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